I tried fixing the doom3config.cfg file, to the resolution and everything. But its not showing in the game UI where video settings are located. I tried setting the AA on x8, and still nothing. It's horrible to play this game on such a low resolution.

Another thing, Sikk mod looks all blurry and dark. The settings is really confusing in the mod.

I used that guide and had no problems running at 1920x1080. The thing is, you just set it in the config and start playing the game. If I remember, even when I was at 1920x1080 the options menu said 640x480. And if I remember, even just going to the options menu for video and backing out of it would reset the resolution to default.

So follow that guide, then don't bother with the options menu. If that's what you did and it's still not working, let me know and I'll head over to my gaming rig to check out what I have in my config.

richard.eid is right. If you change the config file properly, you'll get 1920 x 1080 resolution when playing the game. The option screen will still reflect 640 x 480, but you'll be playing in widescreen. However, just going into video options and backing out won't disable it; just don't apply any settings changes from there.